This project consists of a series of studies that are designed: 1. To extend our knowledge of the relationship between training structures and demonstration of performances showing the development of equivalence. 2. To determine whether instructions containing stimulus names account for the high probability of equivalence class development we have observed when the comparison as node (CaN) training structure is used with instruction. 3. To determine whether the probability of class development with training structures other than CaN can be increased with instructions that suggest verbal "maps" more illustrative of the intended class structure than those imparted by our previous instructions. 4. To determine whether the facilitative effects of instructions within and across subjects are related to the sophistication of the subjects' language. Our previous research has demonstrated that when persons with retardation are taught the conditional discriminations presumed to be sufficient for the development of equivalence classes, they are more likely to demonstrate such classes if they are taught to select a single comparison stimulus in response to 3 or 4 sample stimuli (CaN training structure) than if they are taught to select 3 or 4 comparison stimuli in response to a single sample (SaN training structure). The first series of studies of the proposed project will include experiments to further analyze this difference and extend the investigation to a teaching structure in which, after the first conditional discrimination, each successive discrimination is linked to the previous discrimination by the use of the previous choice stimuli as samples. Our previous research also suggests that verbal instructions affect the probability of equivalence classes being demonstrated. Our second series of studies is designed to determine how different instructions affect the probability of persons with mild and moderate retardation demonstrating equivalence. Our third series of studies is designed to determine how to teach subjects verbal skills that will allow them to demonstrate equivalence classes even when they encounter nonoptimal teaching structures. Finally, we will analyze the subjects' language skills to determine if there are interactions between language skill level and the effects of instructions.